λ/4-shifted DFB laser/electroabsorption modulator integratedlight source for multigigabit transmission

High-speed, low-chirp, and low voltage driving characteristics of 1.55-μm λ/4-shifted distributed-feedback (DFB) laser/InGaAsP electroabsorption modulator integrated light sources are reported. By optimization of the composition and thickness of the modulator waveguide, the driving voltage for a 10-dB extinction ratio was reduced to 1.4-3 V, depending on the modulator length in the range of 240-125 μm. High-speed modulation up to 10-Gb/s NRZ modulation was achieved by the integrated device with a 125-μm modulator length. The linewidth enhancement factor of the integrated modulator was estimated to be 0.15-0.48     

Dependence of high-speed properties on the number of quantum wellsin 1.55 μm InGaAs-InGaAsP MQW λ/4-shifted DFB lasers

The dependence of intrinsic dynamic properties, such as relaxation oscillation frequency, damping K-factor, and spectral chirping under 10-Gb/s direct modulation, on the number of quantum wells is systematically investigated in 1.55-μm multiquantum-well λ/4-shifted distributed-feedback lasers. The theoretical and experimental results indicate that the dependence of the above three factors on the number of quantum wells is clearly explained by the linear gain saturation of the quantum-well lasers     

Ultralow chirp and high-speed 1.55 μm multiquantum wellλ/4-shifted DFB lasers

An ultra-low-chirp, high-speed, 1.55-μm, multi-quantum-well (MQW), λ/4-shifted, InGaAsP distributed-feedback (DFB) laser is demonstrated. A record chirp width of 0.4-0.5 nm (20-dB down full width) is achieved at 10-Gb/s direct modulation. This low-chirp single-longitudinal-mode operation is attained by an increase in the quantum size effect in the MQW active layer     

16 Gbit/s transmission experiments using a directly modulated 1.3μm DFB laser

A 16 Gb/s electrically time-division-multiplexed lightwave link is discussed. The 16 Gb/s electronic signal was generated by multiplexing together eight copies of the 2-Gb/s pseudorandom sequence (length 2¹⁵-1) produced by a commercial BER test set. A 22-km transmission distance was achieved using a directly modulated, 1.3-μm wavelength DFB laser and a 50-Ω p-i-n receiver. Receiver sensitivity for a BER of 10^-9 was -2.0 dBm. The addition of an optical preamplifier required a more sensitive receiver to avoid saturation-induced distortion in the preamplifier. This was accomplished by reducing the 2-Gb/s word length to 24 b, thereby lowering the intersymbol interference penalty and effectively increasing the receiver sensitivity. Under these conditions, the optical preamplifier receiver sensitivity was -19 dBm, and a 64.5-km transmission was demonstrated     

1.5-µm λ/4-shifted InGaAsP/InP DFB lasers

A single wavelength light source in 1.5-μm range was developed using InGaAsP/InPlambda/4-shifted distributed feedback (DFB) semiconductor heterostructures. Superiority of thelambda/4-shifted DFB structure in terms of stability of the main mode at the Bragg wavelength was shown theoretically, in which the threshold, the output, and the polarization characteristics were taken into account. Alambda/4-shifted corrugated grating was made by a newly developed negative and positive photoresists technique. Buried heterostructure (BH) diode lasers with nonreflective window ends were fabricated and highly stable single-mode operation with a low threshold was obtained reproducibly. Direct modulation properties and life-tests results indicated that thelambda/4-shifted DFB lasers could be a reliable single-mode light source in a long span lightwave transmission system in 1.5-μm range.     

1.5 μm λ/4 shifted multiple quantum well distributedfeedback laser diodes

1.5 μm λ/4 shifted multiple quantum well distributed feedback laser diodes have been achieved for the first time. A characteristic temperature value for a threshold current at around room temperature was as high as 88 K. Spectra at 0.9 times the threshold current showed substantial TM mode suppression. The MQW active region consists of four GaInAs wells (75 Å thick) and GaInAsP barriers (λ_g=1.15 μm, 150 Å thick) grown by metalorganic vapour phase epitaxy (MOVPE). 1.3 μm GaInAsP was grown as an optical guide layer     

Analysis of surface-emitting λ/4-shifted DFB lasers with adistributed Bragg reflector

Threshold current density and differential quantum efficiency are analyzed for a surface emitting (SE) λ/4-shifted distributed feedback (DFB) laser consisting of alternating active and passive layers with a distributed Bragg reflector (DBR). It is shown that the threshold current density can be reduced by using the DFB action induced by alternating active and passive layers in the active region of the SE DFB laser structure, as compared to SE DBR lasers with a homogeneous active region. It is also shown that the differential quantum efficiency of the DFB laser with a DBR can be higher than that of conventional DBR lasers without increasing the threshold current density     

Analysis of wavelength conversion using highly nondegeneratefour-wave mixing in λ/4-shifted DFB lasers

We present a theoretical analysis of terahertz-range wavelength conversion using highly nondegenerate four-wave mixing in λ=1.55 μm, medium-coupling λ/4-shifted distributed feedback (DFB) lasers. Based on the coupled-wave approach, our model predicts up to ~2 THz probe-pump detuning with a -20 dB or higher conversion efficiency for quantum-well λ/4-shifted DFB. The influences of pump power and DFB coupling strength (κL) on wave mixing as well as the Bragg reflection effects are discussed. The predictions of the model are found to be in good agreement with recent experimental observations     

AlGaInAs/InP 1.5 μm MQW DFB laser diodes exceeding 20 GHzbandwidth

Buried mushroom multiquantum well DFB laser diodes with compressively strained GaInAs quantum wells and asymmetric confinement layer design are fabricated with a combined MBE/MOCVD technology. Packaged devices exhibit high -3 dB IM bandwidths for very low bias levels and a record bandwidth for this material system of 21 GHz     

Complex-coupled λ/4-shifted DFB lasers with a flat FMresponse from 10 kHz to 17 GHz

Semiconductor lasers with a flat FM response are required for coherent FSK transmission systems. A complex-coupled λ/4-shifted DFB laser is described that gives a flat FM response from 10 kHz to I7 GHz at 15 mW, achieved by using the self-suppressing mechanism of the spatial hole-burning effect     

High-temperature CW operation of planar buried-ridge structurelasers at λ=1.5 μm

GaInAsP/InP-PBRS lasers emitting at 1.5 μm have been fabricated by multiple liquid-phase epitaxy. Effective current confinement is achieved without current blocking layers. CW threshold current is as low as 9 mA at 25°C. Output powers per facet of up to 10 mW at 80°C and 3.5 mW at 100°C are obtained. The maximum operation temperature of 110°C is the highest value yet achieved with this type of laser at 1°5 μm     

All-optical timing extraction using a 1.5 μm self pulsatingmultielectrode DFB LD

All-optical timing extraction from an intensity modulated 196 Mbit/s return to zero optical data stream by the injection locking technique, using a 1.5 μm self-pulsating multielectrode DFB laser diode (LD) is demonstrated. A frequency lock-in range, which depends upon both the injection signal level and the length of space continuation is investigated     

High-speed 1.5 μm self-aligned constricted mesa DFB lasers grownentirely by MOCVD

Ultrahigh-speed 1.5 μm wavelength self-aligned constricted mesa GaInAsP-InP distributed-feedback lasers grown entirely by low-pressure metalorganic chemical-vapor deposition are discussed. A self-aligned process was applied to lower the stray InP junction capacitance to as low as 1.6 pF. A record bandwidth of 13 GHz in the 1.5 μm wavelength region was demonstrated     

Stabilization of the longitudinal mode against spatial hole burningin λ/4-shifted DFB lasers by quantum size effect

A novel method for stabilizing the spectral properties of λ/4-shifted distributed-feedback (DFB) lasers against the longitudinal spatial hole burning by using the quantum size effect in MQW structures is proposed and demonstrated experimentally and theoretically. The effect of the longitudinal spatial hole burning on the spectral behavior is shown to be determined by the α parameter, not by the differential index or by the optical confinement in the active layer. The reduction of the α parameter is found to be very effective in suppressing the spectral instabilities induced by the longitudinal spatial hole burning     

λ/4-shifted InGaAsP/InP DFB lasers

lambda/4-shifted InGaAsP/InP DFB lasers were studied theoretically and experimentally. The effect of reflectivities at the end of a DFB region and that of alambda/4shift position were analyzed in terms of stability of single-longitudinal-mode operation and asymmetric power distribution. The shift of thelambda/4-shift position from the center to a certain place in the DFB region, with the end reflectivities less than several tenths of a percent, seemed most effective for efficient power extraction and reproducible DSM operation. The devices emitting at 1.5 μm range were fabricated by using negative and positive photoresists and employing one-step holographic exposure. They exhibited single-longitudinal-mode operations just at or closely around the center of the stopband, i.e., the Bragg wavelength. The slight wavelength deviations from the center were found to be attributed to the accidental phase-shift variations from the optimal value. Concerning such deviations in the fabricated devices, a simple and useful criterion, for example,P_{0}/P_{1} geq 2-3atI/I_{th} = 0.9, for stable DSM operation was presented. Statistically, single-longitudinal-mode operations were observed in 95 devices out of 100, and the theoretical prediction was verified. The side-mode-suppression ratios under high-speed direct modulation were 35 dB or more.     

8 Gbit/s transmission over 76 km of optical fibre using a directlymodulated 1.3 μm DFB laser

The authors report an optical transmission experiment at a data rate of 8 Gbit/s over an unrepeatered distance of 76 km. The transmitter was a directly modulated, 1.3 μm-wavelength, distributed-feedback laser. The receiver employed an avalanche photodiode and a high-impedance GaAs MESFET preamplifier     

Performance of single-electrode 1.5-μm DFB lasers in noncoherentFSK transmission

The author reports the results of an investigation of the performance of single-electrode 1.5-μm DFB (distributed feedback) lasers in 1.7-Gb/s noncoherent frequency-shift-keyed (NC-FSK) transmission. Sixteen commercial laser transmitters were characterized in terms of FSK transmission sensitivity, eye-margin, chromatic dispersion penalty and pattern dependence. Using amplitude-shift-keying (ASK) performance as a baseline, FSK is shown to outperform ASK when dispersion is present, while ASK is slightly better with no dispersion. FSK transmitters with commercial single-electrode DFB lasers are shown to provide an attractive alternative to ASK in dispersion limited systems. The FSK degradations mainly result from an inadequate FM modulation index and a thermal-FM index manifested as a pattern length dependence     

15 Gb/s multichannel optical interconnect laser array transmitteroperating at λ=1.3 μm

We have fabricated and measured detailed bit error rate experiments on a 12 channel optical interconnect transmitter operating at rates up to 1.25 Gb/s per channel, using InGaAsP/InP λ=1.3 μm lasers. The lasers are highly uniform, the channel crosstalk is less than 1 dB, and the mode selective losses are low (<1 dB). This transmitter has been demonstrated in an architecture which would allow the transmission of 120 channels of 100-Mb/s uncompressed video signals     

Asymmetric λ/4-shifted InGaAsP/InP DFB lasers

1.5 μm asymmetriclambda/4-shifted InGaAsP/InP DFB lasers, in which thelambda/4-shift position was moved from the center of the DFB region toward the front side, were made in order to obtain higher output power with high single-longitudinal-mode (SLM) yield. Statistical measurements revealed that it was effective for the increase of the differential quantum efficiency from the front facet without a remarkable decrease of the SLM yield to move thelambda/4-shift position to the front facet by 10-15 percent of the total DFB length. The output efficiencies of the diodes with AR coatings on the window structure were almost coincident to those expected from theoretical calculations. The main to submode ratioP_{0}/P_{1}in the rear spectra of the asymmetric devices noticeably decreased with increasing asymmetry. From an experimental point of view, a criterion for stable SLM operation, for example,P_{0}/P_{1} gsim 1.5in the rear spectrum atI = 0.9 Ithfor thelambda/4-shift positionl_{f} : l_{r} = 35 : 65, is presented.     

Application of a λ/4-shifted DFB laser/electroabsorptionmodulator monolithically integrated light source to single-chip pulsegenerator with variable repetition rate

The authors have demonstrated the application of a 1.55-μm λ/4-shifted DFB laser/InGaAsP electroabsorption modulator monolithically integrated light source to a single-chip pulse generator with variable repetition rate for soliton transmission for the first time. Quasi-transform-limited pulses with a time-bandwidth product of 0.31 were successfully generated up to 8.6-GHz repetition rates by the sinusoidally driven integrated modulator having high modulation efficiency of 13 dB/V. No change of lasing wavelength was observed in the operation scheme of the integrated device as a pulse generator